/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.method.annotation;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.context.request.NativeWebRequest;

import javax.servlet.ServletException;

/**
 * Resolves method arguments annotated with {@code @Value}.
 *
 * <p>An {@code @Value} does not have a name but gets resolved from the default
 * value string, which may contain ${...} placeholder or Spring Expression
 * Language #{...} expressions.
 *
 * <p>A {@link WebDataBinder} may be invoked to apply type conversion to
 * resolved argument value.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public class ExpressionValueMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {

    /**
     * Create a new {@link ExpressionValueMethodArgumentResolver} instance.
     *
     * @param beanFactory a bean factory to use for resolving  ${...}
     *                    placeholder and #{...} SpEL expressions in default values;
     *                    or {@code null} if default values are not expected to contain expressions
     */
    public ExpressionValueMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {
        super(beanFactory);
    }


    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(Value.class);
    }

    @Override
    protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
        Value ann = parameter.getParameterAnnotation(Value.class);
        Assert.state(ann != null, "No Value annotation");
        return new ExpressionValueNamedValueInfo(ann);
    }

    @Override
    @Nullable
    protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest webRequest) throws Exception {
        // No name to resolve
        return null;
    }

    @Override
    protected void handleMissingValue(String name, MethodParameter parameter) throws ServletException {
        throw new UnsupportedOperationException("@Value is never required: " + parameter.getMethod());
    }


    private static final class ExpressionValueNamedValueInfo extends NamedValueInfo {

        private ExpressionValueNamedValueInfo(Value annotation) {
            super("@Value", false, annotation.value());
        }
    }

}
